Muffler for fluid actuated tool



Sept. 1,1970 V iw ETAL 3,526,293

MUFFLER FOR FLUID ACTUATED TOOL Filed June 13, 1968 2 Sheets-Sheet 1 ROY J. HAYES ARNOLD E. RAPP INVENTORS ATTORNEY p 7 R. J. HAYES ETAL 3,526,293

MUFFLER FOR FLUID ACTUATED TOOL Filed June 13, 1968 2 sheets-sheet z United States Patent US. Cl. 181-36 9 Claims ABSTRACT OF THE DISCLOSURE A mufller system for a fluid actuated tool including inner and outer flexible conduits arranged in telescoped relation with the upstream end of the inner conduit connected to the exhaust port of the tool. The outer conduit is in surrounding relation with the inner conduit and the downstream end of the inner conduit is closed. Longitudinally spaced perforations in the inner conduit communicate exhaust fluid from the interior of the inner conduit to the interior of the outer conduit; however, a substantial longitudinal segment of the downstream end of the inner conduit is imperforate and functions as an acoustical filter. The downstream end of the outer hose is connected to another acoustical filter which opens to the atmosphere.

BACKGROUND OF THE INVENTION Pressure fluid actuated percussive tools of the expansible chamber type emit exhaust pulses which create objectionable noise in and around working areas. Heretofore proposed exhaust mufliing devices for such tools generally involve one of the following noise abatement concepts:

(1) Sound absorbing and diffusion structures and materials are attached to the tool exhaust port to attenuate exhaust pressure pulses before they reach the surrounding atmosphere.

(2) A chamber of sound absorbing, flexible material is jacketed about the body of the tool for receiving and expanding the exhaust fluid prior to emission to atmosphere.

(3) Exhaust fluid is conducted a substantial distance away from the work area by means of a pipe or other suitable conduit so that noise-producing expansion of the exhaust fluid to atmosphere occurs at a location remote from the tool operating personnel.

Each of the above enumerated concepts provides some degree of muflling action; however, each displays certain practical shortcomings when applied to many kinds of fluid actuated tools. For example, fabricated mufller devices attached to the body of a percussive tool tend to vibrate loose and are subject to damage in the course of normal rough usage of such tools. Muflier jackets made of rubber or the like are likewise subject to damage and are diflicult to assemble and disassemble. Both fabricated mufflers and muffler jackets tend to plug up due to the formation of ice particles as the exhaust fluid rapidly expands and entrained moisture cools below the freezing point.

A simple hose or pipe to be effective as a noise abatement device must transport the exhaust a distance from the tool to some suitably remote point where exhaust noise can be tolerated. In underground mining operations and in urban areas, for example, it may not be practical to use hoses or pipes of the length required. Moreover, if the tool is to be moved about from place to place on a mobile carriage, as in the case of portable drilling rigs and mining jumbos, it would be inconvenient to drag a long length of exhaust hose about the work site.

An object of this invention is to provide an improved tool exhaust system of the piped-away type which employs a flexible hose assembly which itself has selected acoustical properties and which is terminated with an acoustic filter device.

SUMMARY OF THE INVENTION In accordance with the present invention, a deicing fitting, a flexible hose assembly and an acoustical filter are connected in series to receive exhaust fluid from a pressure fluid actuated tool. The fitting provides a swivel connection between the tool exhaust port and the hose assembly; and, the swivel fitting also functions to prevent ice accumulation in the bend of the fitting by means of exhaust-induced vibrations of a flexible deicing sleeve disposed inside the fitting. The hose assembly is provided with preselected acoustic properties which attenuate the exhaust pressure pulses; and, since the hose assembly per se comprises an effective noise muflling device, it may be relatively short and need not terminate at a point considerably distant from the working area as is the case with an ordinary hose or pipe. The downstream end of the hose mufller opens into an acoustical filter of the expansion chamber type which provides additional muflling before the exhaust fluid passes to atmosphere. The combined noise abatement effects produced by the hose mufller and the acoustical filter are sufficient in observed cases to permit locating the filter in the immediate vicinity of drill operating personnel. In the case of a rock drilling rig or a tunneling jumbo, the acoustical filter may be mounted upon the drill feeding and guiding support; and, the hose connecting the drill and the filter need be only long enough to permit the drill to travel along the support between opposite operating limits. In no event need the hose be drug about, thereby, abrasion of the hose and entanglement of the hose is avoided.

Thus the present invention contemplates a type of pipedaway exhaust system including a flexible conduit which is structurally devised to serve as a muffler and which is attached at one end to a fluid actuated tool slidably mounted on a support and at the other end to an acoustical filter attached to the support.

This invention also avoids troublesome icing of the exhaust conducting components of the improved muflling system. As mentioned above, the swivel fitting connecting the hose assembly to the drill has a flexible internal sleeve which vibrates thereby preventing ice accumulation in the elbow of the fitting. The acoustical filter at the downstream termination of the hose mufifler assembly has a closure member which opens automatically should exhaust pressure increase above a predetermined value due to ice blockage of the holes in the filter which normally pass exhaust fluid to atmosphere. The hose mufiler assembly itself has anti-icing characteristics due to the flexibility of the hose components and due to exhaust pulse-induced vibration of the telescoping hose components.

These and other more detailed objects and advantages of the invention will appear upon reading the following detailed description and upon considering in connection therewith the attached drawings in which:

FIG. 1 is a fragmentary plan view of a percussive tool mounted on a vertical support and shows the elements of the mufller system;

FIG. 2 is a fragmentary view of the tool shown in FIG. 1 wherein a portion of the tool is broken away;

FIG. 3 is an enlarged section of the swivel fitting shown in FIG. 2;

FIG. 4 is a longitudinal section of the hose mufller assembly shown in FIG. 1;

FIG. 5 is a sectional view taken generally along lines 55 of FIG. 1;

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 4;

FIG. 7 is a fragmentary section taken along lines 7-7 of FIG. 6; and,

FIG. 8 is a diagrammatic view of the mufller system indicating certain of the acoustical features of the hose assembly.

DESCRIPTION Referring to FIG. 2, the illustrative tool, shown generally at numeral 10, is a conventionally constructed rock drill comprising a cylinder 12 and a hammer 14 the latter being reciprocatively driven for impacting a drill steel 16 to which a rock bit, not shown, is attached. An automatic distributing valve, not shown, admits working pressure fluid to alternate sides of the hammer; and, a fluid exhaust port 20 through the cylinder 12 is periodically uncovered by the hammer for exhausting partially expanded pressure fluid from alternate sides of the hammer to the exterior of the cylinder. Typically, the frequency of such pulses of exhaust fluid is in a range of to 150 cycles per second; however, pressure waves induced at harmonics of these fundamental frequencies at 100 to 1,000 c.p.s., for example, produce objectionable noise. The rapid expansion of exhaust fluid as it passes from the port 20 to atmosphere is known to create shock waves at frequencies above 1,000 c.p.s. which produce what is commonly termed jet noise. It is an object of this invention to provide a rock drill muflling system of the piped away type which will attenuate the exhaust noise from both of the above indicated sources.

Generally, the exhaust system contemplated by this invention comprises a flexible hose muflier having intrinsic sound attenuating characteristics and an acoustical filter connected to the downstream end of the hose mufiier. In the drawings, the hose muffler is indicated in its entirety by numeral 22 and the filter is designated generally by numeral 24. Swivel fittings 26 and 28, respectively, connect the upstream end of hose 22 to the drill 10 and the downstream end of the hose to the filter 24. FIG. 1 of the drawings illustrates one advantageous application of the muffler hose 22 wherein the rock drill 10 is advanceable and retractable along a vertically disposed guide and feed support and, the filter 24 is bolted or otherwise suitably secured at a point intermediate the ends of the support 30. The swivel fittings 26 and 28 facilitate movement of the drill 10 along support 30 between upper and lower operating limits without unduly straining the hose muffler 22.

Referring to FIG. 4, the hose mufiler 22 comprises an outer conduit 32 which receives in telescoped relation an inner conduit 34. The direction of flow of exhaust thrOugh the hose muffler is indicated by arrows as being from fitting 26, through the hose mufl'ler to fitting 28. As best seen in FIG. 3, the upstream ends of both the outer and inner conduits are compressively secured in surrounding relation with the projecting end of fitting 26 by a suitable clamping device 36. The inner conduit 34 has an outer diameter which is smaller than the inner diameter of the outer conduit; and as shown in FIG. 6, the outer and inner conduits coactively define therebetween an annular exhaust passage 38. Although the inner conduit is not supported within the outer conduit 32, the flow of exhaust fluid between these conduits tends to maintain a substantially concentric relation therebetween when the drill 10 is operating. The interior 40 of the inner conduit 34 communicates with the annular passage 38 through a multiplicity of radially opening, angularly spaced apertures 42. The apertures are longitudinally spaced along a substantial segment of the length of the inner conduit 34, in the manner best shown in FIG. 7. Preferably, the diameter of the apertures 42 is just large enough to prevent buildup of exhaust entrained ice particles within the apertures leading to complete blockage. The inner conduit 34 is shorter in length than the outer conduit 32 and is terminated at its extreme downstream end 44 by a plug or other suitable closure means. Between the extreme downstream end 44 of the inner conduit 34 and the farthest downstream apertures 42, the inner conduit wall is imperforate and defines an elongated tubular chamber 46. The downstream end of the outer conduit 32 is compressively attached to the swivel fitting 28 by a suitable clamp 48. That portion of the outer conduit 32 between the end 44 of the inner conduit 34 and the fitting 28 defines a tubular chamber into which the annular passage 38 opens.

The acoustical filter 24 comprises a cylindrical chamber 51 which receives exhaust fluid from the hose mulfler chamber 50 through the fitting 28. The filter 24 is rigidly mounted on the support 30 by means of brackets 52. A plurality of angularly spaced apertures 54 open radially through the cylindrical wall 56 to atmosphere. The upper end of cylinder wall 56 is closed by a plate 58 which is biased by springs 60 into fluid-tight seating engagement with the cylinder wall 56. An internal annular flange 62 inside the cylinder wall 56 carries four bolts 64 which extend upwardly through the plate 58; and, the springs 60 are compressively held between the plate 58 and the heads of the bolts 64. Should the exhaust apertures 54 become blocked by exhaust entrained ice particles, an immediate increase in fluid pressure within the filter 24 will lift the plate 58 from the upper end of the cylinder wall 56 thereby permitting exhaust to escape from chamber 51 to atmosphere. This feature of the present invention prevents deleterious buildup of back pressure on the drill 10 should the mufller system become blocked. As soon as the apertures become cleared, the spring 60 will reclose the plate 58 against the cylinder 56.

Preferably, but not necessarily, the swivel fittings 26 and 28 are constructed as shown in FIG. 3 and as described in detail in US. application Ser. No. 664,864,

, filed Aug. 31, 1967 and entitled Exhaust Pipe Assembly for Pneumatic Tools. Briefly described, the fitting 26 comprises a rigid tubular member 66 and a flexible tubular sleeve 68. Both members 66 and 68 are curved near their midpoints to provide an elbow type swivel. The upstream end of member 66 is swivelly retained in a boss 70 projecting from the cylinder 12; and, the upstream end of the flexible sleeve 68 is clamped to the interior wall of member 66. An annular space 72 is provided between members 66 and 68 which permits the sleeve 68 to flex or vibrate as pulses of exhaust fluid impinge the curved portion thereof. The flexure of sleeve 68 serves to break up and prevent lodging of exhaust carried ice particles within the fitting; and, the resilient sleeve 68 also functions as a sound absorptive lining for reducing exhaust noise transmission to the hose mufller inlet.

The good noise silencing characteristics of the hereinabove described mufller system are attributable to a combination of structural and functional features which dissipate a substantial portion of the sound energy contained in the pulsating fluid exhausted from the tool 10. The flexible conduits 32 and 34 are made from a suitably resilient, yet strong, material such as rubber or neoprene and exhibit acoustic absorptivity over the audible frequency range. Since the conduits 32 and 34 are telescoped, the interior wall of conduit 32 and both the interior and exterior walls of conduit 34 are effective as sound absorbing surfaces. The so-called jet noise of the exhaust fluid which occurs at frequencies generally above 1,000 c.p.s. is reduced substantially due to expansion of the exhaust fluid within the mufller system prior to contact with the atmosphere. Such expansion occurs successively in the inner conduit 34, the annular passage 38, the tubular chamber 50 and the filter 24. Jet noise is further attenuated as the exhaust fluid flow is caused to change direction as it traverses the swivel fittings 26 and 28, the inner conduit apertures 42 and the apertures 54in the acoustical filter 24. The apertures 42 and 54 also tend to scatter or diffuse the exhaust fluid and to convert the pulsating flow into a more continuous flow. As best illustrated in the diagram of FIG. 8, the hose muffler 22 includes the tubular chambers 46 and 50. Chamber 46 functions as a reflective acoustical filter of the side branch type comprising a closed tube which does not have exhaust fluid flowing inside it. The chamber 46 is sized so that several bands of frequencies occurring between 125 c.p.s. and 1,000 c.p.s. are attenuated. The chamber 50 comprises an expansion chamber type of acoustical filter which attenuates transmission of noise below frequencies of 1,000 c.p.s. The filter 24 comprises yet another expansion chamber device which is sized to produce noise-abating counter-pressure waves above 1,000 c.p.s.

From the foregoing detailed description, it will be appreciated that the mufller system contemplated by this invention provides the advantages of piped-away system without having a long, clumsy pipe or hose in the work area. Moreover, the system hereindescribed is particularly well suited to avoid icing problems commonly encountered with pressure fluid actuated tools. Due to the shortness of the hose and its flexibility, this piped-away mufiier system is ideal for use with portable drilling rigs having provision for feeding a drill along a movable mast or guide shell.

Those skilled in the mufliing art will recognize that certain changes may be made in the construction, proportion and arrangemment of parts of the illustrative embodiment without departing from the spirit of the invention. For example, the size and shape of the noise filter elements 24, 46 and 50 should be selected to obtain ptimum noise attenuation for a particular type of tool having known exhaust noise characteristics.

Having disclosed the invention in full, we claim:

1. A mufller for the exhaust of a pressure fluid actuated device, comprising:

(a) an outer conduit;

(b) an inner conduit having an exhaust fluid receiving end and a closed end;

(c) the conduits comprising flexible rubberlike materials having good sound absorptivity;

(d) the conduits being in telescoped relationship and defining a passage therebetween;

(e) the inner conduit having a perforated segment for passing exhaust fluid from the inner conduit to the passage;

(f) the inner conduit having an imperforate segment adjacent the closed end thereof; and

(g) the outer conduit having an exhaust opening to its exterior.

2. A fluid actuated tool;

a support slidably mounting the tool;

a hose type, flexible muffler having one end connected to the tool for receiving exhaust fluid therefrom;

the other end of the flexible muflier being connected to the support; and

said flexible muflier comprising:

an outer conduit;

an inner conduit having an exhaust fluid receiving end and a closed end;

the conduits being in telescoped relationship and defining a passage therebetween;

the inner conduit having a perforate segment for passing exhaust fluid from the inner conduit to the passage;

the inner conduit having an imperforate segment adjacent the closed end thereof; and

the outer conduit having an exhaust opening to its exterior.

3. The invention set forth in claim 1, wherein the longitudinal segment of the outer conduit between the closed end of the inner conduit and the exhaust opening from the outer conduit comprises a tubular acoustical filter.

4. The invention set forth in claim 1, wherein an acoustical filter comprising a hollow container is connected to the exhaust opening of the outer conduit.

5. The invention set forth in claim 4, wherein the hollow container is provided with a movable member which opens and closes in response to exhaust pressure changes inside said container.

6. The invention set forth in claim 5, wherein the closure member is spring biased and is held in a closed condition when exhaust pressure in the container fails to overcome such spring bias.

7. The invention set forth in claim 1, wherein each of the conduits has at least one of its ends opening to a swivel fitting.

8. A fluid actuated tool;

a support slidably mounting the tool;

a hose type, flexible mufller having one end connected to the tool for receiving exhaust fluid therefrom; the other end of the flexible mufller being connected to the support;

said mufller comprising inner and outer conduits of rubberlike material having good sound absorptivity; said inner conduit having a closed end; and means communicating the interiors of said conduits with one another.

9. The invention defined in claim 8, wherein:

(a) an accoustical filter is mounted on the support;

and

(b) the other end of the flexible mufller is connected to the acoustical filter.

References Cited UNITED STATES PATENTS 2,028,320 1/1936 Curtis 18l36 2,964,120 12/ 1960 Graham 181-47 3,323,305 6/1967 Klees 181-47 3,285,395 5/1968 Kurt et a1 181-36 FOREIGN PATENTS 796,067 1/ 1936 France.

776,884 6/ 1957 Great Britain.

842,192 7/1960 Great Britain.

919,477 2/ 1963 Great Britain.

ROBERT S. WARD, JR., Primary Examiner US. Cl. X.R. l8l-47, 53, 59 

